'Dolmetschen' appears to be a loanword into German from the Turkic languages. From Wiktionary:

From Middle High German tolmetsche. Compare Proto-Slavic *t?lmac? (“interpreter”) (Russian ?????´? (tolmác),Polish tlumacz), Hungarian tolmács, borrowed from a Turkic language, from Proto-Turkic *tilmaç (cf. Turkish dilmaç (“translator, interpreter”)).